1. Field of the Invention
The present invention pertains to an electrostatic chuck used to hold substrates in position during semiconductor processing. The electrostatic chuck is capable of functioning at temperatures greater than 175.degree. C., and preferably greater than 300.degree. C. The electrostatic chuck includes at least one conductive layer positioned between two Polyimide comprising dielectric layers. A specially designed electrical connector capable of operating at the same elevated temperatures is used to supply power from a high DC power source to the conductive layer within the electrostatic chuck.
2. Brief Description of the Background Art
Electrostatic chucks are devices which have gained wide usage in the semiconductor field for clamping semiconductor wafers during manufacturing processes. These chucks eliminate the need for mechanical clamping mechanisms, which are often clumsy and induce contamination into processing chambers. In addition, a clamping mechanism rests on the surface of the substrate and prevents full face utilization of the surface of the substrate. The most popular electrostatic chucks are multilayered structures fabricated using polyimide for the dielectric layers. Polyimide has desirable properties such as high temperature stability (relative to other organic polymers), good dielectric behavior, and excellent mechanical properties. To date, such electrostatic chucks have been used primarily in plasma etching processes, since these processes are carried out at about 130.degree. C. or less. The 130.degree. C. temperature is about the maximum sustainable operational temperature for electrostatic chucks fabricated from conventional polyimides used in combination with non-polyimide adhesive layers. For example, a non-polyimide adhesive layer is frequently used to attach the bottom polyimide of an electrostatic chuck to an underlying metallic pedestal. The underlying pedestal or platen is used to support the semiconductor substrate, to provide heating and cooling of the substrate, and to act as an electrode in many applications.
U.S. Pat. No. 4,645,218 to Ooshio et al., issued Feb. 24, 1987, describes an electrostatic chuck having: an electrostatic attraction body; an electrostatic conductive support body for supporting the electrostatic attraction body; channels for passing cooling medium through the support body; and, a means for covering the exposed surfaces of the support body, except the portion over which the workpiece is placed. The electrostatic attraction body comprises an insulation layer and an adhesive layer which bonds the insulation layer to an underlying platen or pedestal. The insulation layer is a three film composite having a polyimide or polyester upper and bottom dielectric film with an electrode film sandwiched between the upper and bottom dielectric films. The electrostatic chuck is said to be used in a process apparatus such as a dry-etching apparatus, with no reference given as to operational temperatures.
U.S. Pat. No. 4,897,171 to Tadahiro Ohmi, issued Jan. 30, 1990 discloses a wafer susceptor capable of adsorbing a wafer by an electrostatic force and of regulating an electric potential of the wafer to a predetermined value in time. The susceptor comprises a first conductive electrode which includes its flat surface covered with a thin insulating film; a second conductive electrode which is electrically insulated from the first conductive electrode and is disposed so that its surface is flush with the surface of the thin insulating film which covers the first conductive electrode; a means for imparting a specified electric potential to the second conductive electrode; and a means for applying a predetermined voltage between the first conductive electrode and the second conductive electrode.
U.S. Pat. No. 5,221,403 to Nozawa et al., issued Jun. 22, 1993, describes a wafer support table used in a vacuum chamber of a magnetron plasma etching apparatus. The wafer support table includes a member having an electrostatic chuck for supporting the wafer on its upper surface. The electrostatic chuck is constituted of two insulating sheets (polyimide, for example) having an electrically conductive sheet positioned between the insulating sheets. The electrically conductive sheet consists of copper, for example. The maximum operational temperature given is 70.degree. C. to 80.degree. C.
U.S. Pat. No. 5,250,137 to Arami et al., issued Oct. 5, 1993, describes a plasma etching apparatus including an electrostatic chuck constructed of two insulating films having a conductive layer sandwiched therebetween. The conductive layer is said to be made of copper, for example, with the insulating films being made of polyimide, for example. A power supply head is also described which includes a coil spring within an insulating cylindrical body, where the coil spring serves to push upward the power supply head to permit connection of the head to an exposed conductive layer within the electrostatic chuck. No particular temperature of operation is described or claimed.
U.S. Pat. No. 5,275,683 to Arami et al., issued Jan. 4, 1994, discloses a wafer mount useful in a plasma etching apparatus. The mount includes an electrostatic chuck member arranged on top of a susceptor, the electrostatic chuck member having a rim which is curved downward along the curved rim section of the susceptor, departing from the marginal portion of a semiconductor wafer mounted thereon. The electrostatic chuck sheet is said to comprise a pair of polyimide resin films with a thin conductive film such as a copper foil sealed between the polyimide resin films. The films are particularly recommended to be made of a non-crystallized aramid resin having a thickness of about 50 .mu.m, as an alternative to a polyimide resin. The maximum temperature discussed is about 35.degree. C.
U.S. Pat. No. 5,314,573 to Higuchi et al., issued May 24, 1994, describes a dry etching method for anisotropic etching of a semiconductor wafer. The apparatus used comprises an electrostatic chuck having a chuck body constituting the lower electrode, and an electrostatic suction sheet which is flexible and disposed to cover the upper surface of the chuck body. The electrostatic suction sheet included two insulating polyimide sheets and a conductive sheet interposed between the two polyimide sheets. The two polyimide sheets are fused to each other such that the fused portion covers the periphery of the conductive sheet. The maximum operational temperature described for use of the electrostatic chuck is about 130.degree. C.
Although electrostatic chucks using polymeric insulating layers are frequently described for plasma etching at temperatures of 130.degree. C. or less, they have not been described for use at higher temperatures, to the knowledge of applicants. This is due principally to performance limitations of the polymeric adhesives used to attach them to an underlying substrate surface. In any case, it would be highly advantageous to have an electrostatic chuck capable of functioning at temperatures of 200.degree. C. or higher which is fabricated from polymeric insulating layers which tend to be less expensive and offer improved flexibility over ceramics and various oxides which might be used as an alternative.